These studies will examine the adult structure of the visual cortex (area 17 and 18) of the macaque monkey in Golgi preparations and using the electron microscope. The structure of these areas in the macaque will be compared with the visual cortex of cat and tree shrew cortex. The effects of visual deprivation and prevention of normal binocular vision on the structural development of the macaque area 17 and development of connections by the corpus callosum will be assessed. The visual system of the rat will be used as a model to determine factors governing development, distribution and degree of plasticity of different groups of optic nerve fibers. This work should provide a morphological background to physiological studies on mature, developing and visually deprived primate cortex. The developmental approaches should give a baseline for understanding the nature and causes of defects in the visual system arising during early formation of neuronal connections.